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The influence of the addition of carbon using methane or methanol/water to an inductively coupled plasma (ICP) via the carrier gas flow on the sensitivity in laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS) was studied. During the ablation of SRM NIST 610 with simultaneous addition of CH(4) (0.6-1.4 ml min(-1)), a sensitivity enhancement of more than one order of magnitude for selected analytes (e.g. (75)As(+)) was observed. In addition to the sensitivity enhancement for As, Te, I and Se, also all other measured elements showed a significantly enhanced sensitivity (minimum by a factor of 2). Potential mechanisms for the observed intensity enhancement include charge transfer reactions, a change in the ICP shape and a temperature increase in the plasma. Furthermore, the aspiration of a methanol-water mixture into a cooled spray chamber and the simultaneous addition to the laser ablated aerosol was investigated. This type of mixing leads to a sensitivity enhancement up to a factor of 20. To prevent clogging of the sampler cone and skimmer cone by carbon deposition, a fast cleaning procedure for the interface is tested during running ICP, which allows the application of such a set-up for specific applications.

Whereas colored andesine/labradorite had been thought unique to the North American continent, red andesine supposedly coming from the Democratic Republic of the Congo (DR Congo), Mongolia, and Tibet has been on the market for the last 10 years. After red Mongolian andesine was proven to be Cu-diffused by heat treatment from colorless andesine starting material, efforts were taken to distinguish minerals sold as Tibetan and Mongolian andesine. Using nanosecond laser ablation-inductively coupled plasma mass spectrometry (ICPMS), the main and trace element composition of andesines from different origins was determined. Mexican, Oregon, and Asian samples were clearly distinguishable by their main element content (CaO, SiO(2) Na(2)O, and K(2)O), whereas the composition of Mongolian, Tibetan, and DR Congo material was within the same range. Since the Li concentration was shown to be correlated with the Cu concentration, the formerly proposed differentiation by the Ba/Sr vs. Ba/Li ratio does not distinguish between samples from Tibet and Mongolia, but only between red and colorless material. Using femtosecond laser ablation multi-collector ICPMS in high-resolution mode, laboratory diffused samples showed variations up to 3‰ for (65)Cu/(63)Cu within one mineral due to the diffusion process. Ar isotope ratio measurements proved that heat treatment will reduce the amount of radiogenic (40)Ar in the samples significantly. Only low levels of radiogenic Ar were found in samples collected on-site in both mine locations in Tibet. Together with a high intra-sample variability of the Cu isotope ratio, andesine samples labeled as coming from Tibet are most probably Cu-diffused, using initially colorless Mongolian andesines as starting material. Therefore, at the moment, the only reliable source of colored andesine/labradorite remains the state of Oregon.

The potential of femtosecond laser ablation multi-collector inductively coupled plasma mass spectrometry (fs-LA-MC-ICPMS) for in situ analysis of U-Th disequilibria in titanite was investigated. The aim of the study was to resolve spatial variations in ( 230 Th/ 238 U) ratios (where parentheses denote activity) in titanite from slowly cooled magma bodies. An in-house titanite glass (TG2), determined to be in secular equilibrium by solution mode MC-ICPMS (i.e. ( 230 Th/ 238 U) ¼ 1), was used to correct for U-Th elemental fractionation by sample standard bracketing. The effect of instrument operating conditions on the accuracy and reproducibility of ( 230 Th/ 238 U), ( 232 Th/ 238 U) and ( 230 Th/ 232 Th) ratios was studied by analyses of titanite minerals with known composition and a secondary titanite glass standard. The ( 230 Th/ 232 Th) data were found to be accurate and reproducible, independent of the instrument setting used, suggesting that corrections made for SEM-Faraday gain and abundance sensitivity were appropriate. However, plasma conditions, laser ablation mode, laser energy and wavelength, and titanite material properties were all found to variably influence the U-Th elemental fractionation and compromise the accuracy of the ( 230 Th/ 238 U) data to different extents. Hot plasma conditions significantly reduce the fractionation between U and Th. A drift in elemental fractionation was observed during single spot analyses using NIR laser ablation and results in errors of up to 29% on the ( 230 Th/ 238 U) data. The magnitude of the drift in the elemental fractionation was different for different laser wavelengths and energies. Ablation using the UV single spot mode was significantly less affected by variable elemental fractionation compared to NIR spot analyses, but precision was limited by lower sample uptake. Scanning mode analyses were not compromised by temporal variation of the U-Th intensity ratios but the degree of elemental fractionation was variable between analyses of different materials (e.g. glass versus minerals). This observation suggests material-dependent differences in U-Th fractionation even for near identical titanite compositions. Analyses of the secondary titanite glass standard TG1 bracketed by TG2 yield the most reproducible and accurate ( 230 Th/ 238 U) data, indicating more adequate correction for elemental fractionation when the calibration standard is matched in terms of material composition and structure.